1. Field of the Invention
The present invention relates to a bending-resistant flexible flat cable (hereinafter referred to as FFC) widely used as a wiring material for movable parts in circuits of electric and electronic equipments, and the production process thereof.
2. Prior Art
The FFC heretofore widely used as a wiring material for movable parts in circuits of electric and electronic equipments is a wire in a thin tape form having a thickness of about 0.3 mm, as shown in FIG. 1 to FIG. 3. This FFC is manufactured by feeding straight a conductor group xe2x80x9c2axe2x80x9d formed by a singular to several tens of conductors xe2x80x9caxe2x80x9d arranged parallel with each other, putting this conductor group 2a between nonconductive plastic films xe2x80x9cbxe2x80x9d with adhesives from upper and lower side thereof, and laminating this with a pair of upper and lower hot rolls xe2x80x9ccxe2x80x9d.
A nonconductive plastic tape xe2x80x9cexe2x80x9d is passed through an adhesive tank xe2x80x9cdxe2x80x9d, so that the plastic film xe2x80x9cbxe2x80x9d of the upper side is obtained in accordance with the coating of adhesive at least on an inner surface of the plastic tape xe2x80x9cexe2x80x9d.
Such a FFC in a tape form has normally excellent flexibility. Hence, this is necessary and indispensable, particularly as a wiring material for cable reel type rotating connectors of automobile airbags, other than wiring materials for movable parts in circuits of electric and electronic equipments.
This is used by storing the FFC in a curled or U-shaped form in a steering case, wherein bending life of about 1xc3x97106 to 5xc3x97106 is required in the bending radius R of from 5 to 15 mm in the temperature range of about xe2x88x9240 to 85xc2x0 C. (the U-shaped sliding and bending test: in accordance with JIS-C5016).
Recently, automobile airbags having high functions such as it finely controlling the way of swelling of the airbag depending on the energy at the time of collision or the weight of a driver have been developed, which entail a so-called multi-conductor FFC, in which the number of conductors is increased to higher than twice the number in the related art. However, as shown in FIG. 4, if the number of conductors is simply increased, the width of the cable increases, and the steering case or the like for storing this becomes also large. Therefore, it can be considered to thin the conductor itself, without changing the width of the cable. However, since heavy current of several amperes is normally applied to the FFC for automobile airbags, generation of heat attributable to an increase in the conductor resistance becomes large, with a decrease of a sectional area of the conductor due to thinning.
Therefore, in order to achieve multi-conductor cables without changing the cable width and the conductor resistance from those of the related art, it is necessary to ensure the same sectional area as that in the related art, by making the thickness of the cable thick and making the conductor thick in the thickness direction.
However, if the thickness of the cable and the conductor is made thicker than that of the conventional FFC, there is caused a problem in that the flexibility which is the largest feature of the flat cable decreases considerably. For example, if the conductor thickness of the FFC is made twice as thick as that of the conventional FFC, the flexibility thereof generally decreases up to one tenth or below, and hence the flexibility required for the FFC for automobile airbags cannot be satisfied.
The present invention has been proposed in order to effectively solve such problems, and it is an object of the present invention to provide a new bending-resistant flexible flat cable that can exhibit flexibility equal to or higher than that of the conventional FFC, even if the number of conductors is increased, and the production process thereof.
In order to solve the above problems, the present invention is a bending-resistant flexible flat cable integrated by sandwiching a single or a plurality of flat type conductors between plastic films with adhesives, wherein the conductor is formed of pure copper having a wiredrawing draught of at least 95% and elongation of at least 5%, or a solution-type high-conductivity copper alloy having a conductivity of at least 70%, the plastic film with adhesives is formed of one having a modulus of longitudinal elasticity of at least 280 kg/mm2 and an elongation of at least 80%, and the 180xc2x0 peel strength between the adhesives of the plastic films with adhesives and the conductor is made to be at least 0.8 kg/cm.
As a result, even if the number of conductors is doubled, while keeping the current value of the conductor resistance, the bending-resistant characteristic equal to or higher than that of the conventional FFC can be exhibited.